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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: Re: rail guns
Message-ID: <8601091435.AA06071@s1-b.arpa>
Date: Thu, 9-Jan-86 08:35:35 EST
Article-I.D.: s1-b.8601091435.AA06071
Posted: Thu Jan  9 08:35:35 1986
Date-Received: Fri, 10-Jan-86 05:34:42 EST
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Organization: The ARPA Internet
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> The major losses would be atmospheric drag, and all the friction of the
> tubes or whatever you are using for "rail guns".

Actually, current rail guns are not very efficient (30%?).  Much of the
energy ends up in a residual magnetic field after the projectile leaves
the launcher.  Using distributed energy input to the gun would help
(this is equivalent to a chemical gun in which the propellant is
distributed along the barrel).

The biggest technical obstacle to rail guns and other electric launchers
is, suprisingly, not the launcher itself but rather the power source.
Launching a 100 kilogram payload to orbital velocity at 1,000 gees
requires a peak power of something like 10 gigawatts (for a brief
time).  The average power will be much less (depending on the launch
rate).  Rail guns could be useful here: an "inverse railgun" can
generate a pulse of power by using a chemical explosion (natural gas
and air, say) to push a metal armature into a magnetic field.
Several thousand such generators would be used in a launcher.